1. Field of the Invention
The present invention relates to an image forming apparatus.
2. Description of the Related Art
Conventionally, an ink jet printer is known as an image forming apparatus for forming an image on a recording medium by ejecting ink drops from the ejection port of an ink head. The ink jet printer is provided with an aspirating mechanism such as an aspirating pump for aspirating ink with an ink viscosity increased by the evaporation of ink solvent at the ejection port of the head or dirt adhered to the ejection port together with the ink. Also, blank ejection to a blank ejection receiver is performed in order to adjust the viscosity of ink and an ink meniscus before the start of printing. Ink aspirated by the aspirating pump or ink blank-ejected onto the blank ejection receiver is collected in a discarded-ink tank.
When a predetermined amount of ink is collected in the discarded-ink tank, the discarded-ink tank is detached from the main body of the apparatus and replaced with a new discarded-ink tank. For example, JP-A-2000-85413 discloses a discarded ink collecting apparatus that senses by an optical sensor and informs a user whether a predetermined amount of ink is collected in a discarded-ink tank. The discarded ink collecting apparatus disclosed in JP-A-2000-85413 is provided with an inflow port for discarded ink at one end portion of the upper wall of the discarded-ink tank and a sensor window at the other end portion. Then, the bottom portion of the sensor window is provided with a white sponge and an optical sensor for sensing light reflected from the sponge. As the discarded-ink tank is filled with the discarded ink, the white sponge provided on the bottom portion of the sensor window absorbs the discarded ink and the color thereof is changed into black whereby the light reflectivity of the sponge becomes a predetermined value or less. As a result, little reflected light enters the optical sensor and it can be sensed that the discarded-ink tank is filled with the discarded ink.
Meanwhile, a water-based ink that contains a pigment and a solvent in which a wetting agent (humectant), a penetrating agent and the like are contained in water is currently being used for printing with satisfactory properties of an image such as a color reproduction property, a fastness property, a light fastness property, an ink drying property, character bleeding, color border bleeding, and a double face printing property, etc., when printing is made on a normal paper.
However, such a pigment-containing ink has a viscosity higher than that of a general dye-containing ink and it takes less time to evaporate the solvent component of the pigment-containing ink so as to reach a viscosity showing the loss of the ink fluidity. Therefore, the discarded ink in the discarded-ink tank has a viscosity showing no fluidity. Also, since it takes less time to evaporate the solvent component of the pigment-containing ink so as to reach a viscosity showing the loss of the ink fluidity, the solvent component may have evaporated to reach a viscosity showing the loss of the fluidity under a high temperature or low humidity environment when the ink is dropped into the discarded-ink tank. Thus, the ink which has reached the viscosity that shows the loss of the fluidity at a stage of dropping the ink into the discarded-ink tank adheres to the discarded ink in the discarded-ink tank as agglomerate. The ink adhering to and deposited to the discarded ink as agglomerate in the discarded-ink tank increases with time. As a result, the discarded ink is not evenly collected in height in the discarded-ink tank but is accumulated in a mountain-like shape such that the top of the mountain is located at the discarded-ink entrance of the discarded-ink tank. Thus, although there is space enough to collect the discarded ink at the end portions of the discarded-ink tank away from the ink entrance thereof, the discarded ink protrudes from the entrance of the discarded-ink tank since the discarded ink is accumulated in a mountain-like shape. When the discarded-ink tank is exchanged on the condition that the discarded ink protrudes from the entrance of the discarded-ink tank, there is a problem in that the circumference of the ink tank in the apparatus is contaminated with the protruded discarded-ink. Also, there is a problem in that the protruded ink clogs the entrance of the discarded-ink tank so that the discarded ink is poured onto the outside of the discarded-ink tank.
However, where a sensing device is provided at the end portion of the discarded-ink tank which is away from the ink entrance on the upper wall thereof, as disclosed in JP-A-2000-85143, a condition cannot be sensed such that the discarded ink does not adhere to the sponge but protrudes from the ink entrance of the discarded-ink tank.
Therefore, an image forming apparatus that can suppress the protrusion of discarded ink from the entrance of a discarded-ink tank is desired.